Over recent years, the use of content delivery networks (CDNs) has grown rapidly. These networks allow content providers to distribute content to consumers. The general principle here is that rather than each user (or consumer, or client) connecting directly to a central server, each client connects to one of many nodes or caches, distributed around the world. Requests from each consumer are routed to an appropriate node, based on the routing policy of the particular network, for example taking into account geographical location of the user and the node, and/or network traffic at each node. Each cache is typically able to either supply the data requested by the consumer, or if it does not have the requested data, forward the request to a node which does have it.